Ch. VII, 3] DISSEMINATION OF PLANTS 



361 



Fig. 258. — Seed of 

 Water Lily, with air- 

 holding coat (aril) . 

 (After Gray.) 



on its surface. Thus the White Water Lily seed has a 

 loose, air-holding extra coat (Fig. 258) and some Sedges 

 have loose-textured carpels, which form efficient floats. 

 Some seeds have flat, corky expansions, as in Iris, while 

 others float by virtue of the unwettable 

 surface they possess. The Nelumbium 

 (the Lotus of ancient literature and art) 

 has a broad, buoyant receptacle (Fig. 

 259), out of which the seeds are said to 

 be dropped from time to time in its 

 decay. Very striking is the case of the 

 Coconut (Fig. 260), in which the ovary 

 develops to a great air-holding husk com- 

 posed of material specially resistant to salt 

 water, although it is now claimed that this plant has been 

 carried by man rather than by drift of ocean currents all 

 around the tropical seas. Ocean currents, indeed, contest with 

 winds for the first place among agencies of plant dispersal. 



5. Carriage by animals. Very important as agents of 

 dissemination, and even of dispersal, are animals, which are 



effective in two different 

 ways. 



First, many fruits or seeds 

 possess structural arrange- 

 ments by virtue whereof they 

 are held attached to the bodies 

 of animals, and are finally 

 dropped far from their places 

 of formation . Especially com- 

 mon are hooks, which become 



Fig. 259. -Floating receptacle of entangled in wool Or fur, 



Lotus (Nelumbium) ; x J. where they often remain until 



the hair is shed. Such hooks 

 have diverse morphological origins; they are developed 

 bracts of the flower head in Burdock (Fig. 261), and out- 

 growths from the ovary wall in Cocklebur (Fig. 262). 



